MXS-1688 Handle ...INTERVAL N <unit>

"INTERVAL N <unit>" is now handled as an expression in itself and
as asuch will cause both statements such as

  "SELECT '2008-12-31 23:59:59' + INTERVAL 1 SECOND;"

and

  "select id from db2.t1 where DATE_ADD("2017-06-15", INTERVAL 10 DAY) < "2017-06-15";"

to be handled correctly. The compare test program contains some
heuristic checking, as the the embedded parser will in all cases
report date manipulation as the use of the add_date_interval()
function.

query_classifier/qc_sqlite/sqlite-src-3110100/src/parse.y

@@ -1948,10 +1948,10 @@ expr(A) ::= expr(X) BITAND|BITOR|LSHIFT|RSHIFT(OP) expr(Y).
 expr(A) ::= expr(X) PLUS|MINUS(OP) expr(Y).
                                         {spanBinaryExpr(&A,pParse,@OP,&X,&Y);}
 %ifdef MAXSCALE
-expr(A) ::= expr(X) PLUS|MINUS INTERVAL INTEGER id. {
+expr(A) ::= INTERVAL INTEGER(X) id. {
   // Here we could check that id is one of MICROSECOND, SECOND, MINUTE
   // HOUR, DAY, WEEK, etc.
-  A=X;
+  spanExpr(&A, pParse, @X, &X);
 }
 %endif
 expr(A) ::= expr(X) STAR|SLASH|REM(OP) expr(Y).